True, but that doesn't mean small amounts won't hurt you. Mercury in particular is so nasty that it's a concern, particularly for nursing mothers, because if mercury transfers to the baby, with a small body mass, it can interfere with brain and nervous system development. I seem to remember that it's basic advice that pregnant or nursing mothers shouldn't eat Great Lakes fish because of the levels of mercury and PCBs.
I read the Washington Post article before I saw this posted on FR. Here's the article:
Report Suggests High PCB Levels in Farmed Salmon
We find in this article that only 7 out of the 10 samples tested had high PCB levels. That's why the statistical significance of only having 10 samples jumps right out. Test 100 samples, from 100 different farms, and then get back to us.
This article does say that the source of the PCBs is the fish meal. Which for me says: switch the farmed fish to vegetable protein! For one thing, it would substantially reduce the demand for the fish that are caught for fish meal, which are important to the whole ocean ecosystem.